Heat Aged Tensile Strength Retention of Poly(p-phenylene terephthalamide) Sewing Thread

The strength retention after exposure to elevated tem-perature in air of continuous filament and staple spun PPTA sewing thread and the precursor yarns was determined. For both types, the process of converting the greige yarn to thread reduced the amount of strength retained after thermal exposure. The continu-ous filament products retained more strength than the staple products. The data was fitted to a kinetic rate model in which two strength loss processes occurred. The first process occurred within about the first 5 minutes of thermal exposure and is hypothesized to be hydrolytic degradation. The estimated secondary degradation process activation energy suggests this to be thermo-oxidative degradation. Optical microscopy of filaments indicates a higher level of kink banding and other damage in continuous filament versus sta-ple products and in finished thread versus the precur-sor yarns. The kink bands and damage are believed to be caused by the staple manufacturing process and the downstream processing of precursor yarn to fin-ished sewing thread. The kink bands and damage are hypothesized to be responsible for the differences in strength retention.